The stress of childcare represents the A variable in the Double ABCX Model.
The ABCX Formula was theorized in the 1950s by Reuben Hill as a stress or crisis-proneness model in family contexts. The formula describes variables which can lead to crises:
This model is often considered flawed because of how inflexible and linear it is. This is why it was expanded upon by Hamilton McCubbin and Joan Patterson during the Vietnam War, when family structures were affected by the absence of a father. McCubbin and Patterson introduced additional elements to the A, B and C components, as well as family coping mechanisms, thus creating the Double ABCX Model.
In this updated model the basic variables are the same, albeit revised. But the A variable still consists of the initial life stressor(s), which corresponds to the strain represented by the need to find chilcare for Karen's baby.